See this FAQ:
https://xoops.org/modules/smartfaq/faq.php?faqid=150

Restore your SQL database
In the new site you will need to have access to your mySQL via the "PHPMyAdmin" application again.
Upload the database by opening the "Run SQL query" window. Select the "database backup" zip file and run the query. The database will be created on the new site.
Now you have to create the same MySQL database user as in the old site and give the correct access rights to the user.

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I did upload the file structure and the database to the new site. I edited mainfile.php. But the new site does not work. I don't know how to "create the same MySQL database user as in the old site and give the correct access rights to the user."

How to setup "Mail setup" in "Preference" (newbb)?

My server gave me:

POP3 Username
POP3 Password
POP3 Server
POP3 Port

How to change the order of forums in newbb?

Inside a category, when I add a forum , it does not go to the place I want...

I changed my password at Cpanel, then the site is down:

This page cannot be displayed due to an internal error.
You can provide the following information to the administrators of this site to help them solve the problem:
Error: Unable to connect to database

what can I do?